The present invention relates to a system and method for minimizing torque disturbances cause by changes in engine operation such as changes in engine air-fuel ratio or injection timing.
Vehicle control systems typically attempt to minimize torque disturbances so that a driver""s comfort and drive feel are not degraded during vehicle operation. One such torque disturbance is when an engine changes air-fuel ratio such as, for example, when changing from lean to rich to release and reduce NOx stored in a downstream catalyst.
One method to minimize such torque disturbances is to change the gear ratio within a single torque path of the transmission. For example, one approach is to change the actual gear ratio of a continuously variable transmission (CVT), as described in U.S. Pat. Nos. 5,243,881, 6,063,004, and 6,188,944. Another such example is to control torque converter lock-up and un-lock action via the torque converter clutch, as described in U.S. Pat. No. 6,079,204.
The inventors herein have recognized a disadvantage with such approaches that attempt to cancel the torque disturbance via adjustments in a single torque path. In particular, these methods require hardware that may not be available on conventional automatic transmissions having only discrete gear ratios. For example, not all vehicles have a CVT. Also, some vehicles may not have a torque converter lock-up clutch.
The above disadvantages are overcome a method for controlling output of a vehicle powertrain having an engine and a torque transmitting unit with multiple transmission paths including multiple clutches, the vehicle also having a electronic control unit. The method comprises: operating the torque transmitting unit to have a preselected gear ratio; providing an indication of an engine output disturbance; in response to said indication, transmitting torque through said torque transmitting unit via at least two paths, and adjusting a clutch parameter of at least one of the clutches of said torque transmitting unit; and after said torque disturbance ends, operating the torque transmitting unit to have said preselected gear ratio.
By adjusting a clutch parameter, for example, clutch hydraulic pressure, it is possible to transmit torque through multiple paths of the transmission in such a way that the change in input torque causes substantially no change in the output torque. In other words, by changing the pressure, and thus the transmitted torque, in response to the torque disturbance changes the way in which torque is transmitted through the unit, and thus changes the net output torque.
In another example, the method comprises: providing an indication of an engine output disturbance; in response to said indication, applying at least two clutches of said torque transmitting unit; and adjusting a clutch parameter of at least one of said at least two clutches based on an estimate of said engine output disturbance.
Again, by using at least two torque paths through the unit, it is possible to compensate for changes in input torque, and thereby provide a substantially constant output torque. I.e., by varying how much torque is transmitted though the two paths (by changing clutch pressure), this varies the effect of a given input torque on the output.
Note that the present invention can be utilized in combination with other methods that attempt to mitigate variations in engine output torque.